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From: uhclem%nemesis@fw.ast.com
To: FreeBSD-gnats-submit@freebsd.org
Subject: SCSI hard disks time out during tape rewind - FDIV039
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>Number:         833
>Category:       i386
>Synopsis:       SCSI hard disks time out during tape rewind - FDIV039
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          closed
>Quarter:
>Keywords:
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Nov 21 20:00:03 PST 1995
>Closed-Date:    Sun Jun 23 22:36:47 PDT 1996
>Last-Modified:  Sun Jun 23 22:37:54 PDT 1996
>Originator:     Frank Durda IV
>Release:        FreeBSD 2.1.0-RELEASE (also FreeBSD 2.0.5-RELEASE)
>Organization:
>Environment:

Three different systems all 486 (25MHz or faster, 8Meg or more RAM,
Adaptec 1540B or 1542CF SCSI adapters, all with latest firmware/BIOS.
At least one SCSI hard disk at aha0:0:0 
SCSI Tape drive always at aha0:2:0
QIC150 using 600ft or longer tape (including 250Meg 1020ft tapes).

Tape drive is QIC-150 Archive Viper 150, or Archive Viper 2150eS, or
WangDAT Model 2600 DAT tape

Normal combinations are:
	33MHz 16Meg 1542CF WangDAT One hard disk
	25MHz 8Meg 1542CF Archive Viper 150 (Internal)
	33MHz 12Meg 1540B Archive 2150eS (external)

>Description:

If the tape is more than 20 seconds or so from BOT and a "mt rewind"
command is issued, after 10 seconds or so the message:
	sd0(aha0:0:0): timed-out
is reported, and continues to be reported at roughly five second
intervals until the rewind is completed and BOT acquired.  On DAT this
operation can take up to a minute.  Note that the tape is st0(aha0:2:0).
On 250Meg (1020ft) QIC tapes, over two minutes can lapse.

During this time, all system SCSI I/O seems to come to a halt.

This problem was not noticed on the SCO UNIX software that used to be 
run on these systems, and we are fairly certain the system didn't
"hang" for a minute when a DAT tape was re-wound as this would have been
noticed.

The higher priority on this report is more out of concern that I/O destined
for the hard disk is aborted or otherwise lost because of the timeouts.
That hopefully isn't the case.

>How-To-Repeat:

On the QIC 150 tape, run it (nrst0) until you hear the drive pause to
reverse direction, then abort the operation.  Now issue a "mt rewind".
On a different screen, type "sync" or do something that will access the
SCSI hard disks.   Within 15 seconds you should see an error on
the console.

On the DAT, I found that writing/reading 50Meg (nrst0) into the tape got you
far enough down the tape to see the error.  Then abort the function
and do a "mt rewind".

>Fix:
	
Issue rewind with bus disconnect commands when allowed.

If these drives can't be disconnected from the bus while performing
rewinds, set time-out timers higher when removable media is present.

It is not sufficient to set longer timers on commands sent just to the
removable media; requests to devices blocked by the slower devices
must also get more time as in the above errors.


>Release-Note:
>Audit-Trail:
State-Changed-From-To: open->closed 
State-Changed-By: gibbs 
State-Changed-When: Sun Jun 23 22:36:47 PDT 1996 
State-Changed-Why:  
The timeout value have been bumped up now. 
>Unformatted:
